1. Field of the Invention
The present invention relates to cost reduction and noise reduction of plasma display devices.
2. Related Background Art
With the decline in prices and the development of high-quality picture technologies, plasma display devices having advantages such as thin bodies and large screen sizes have spread rapidly and have been used widely as large screen television receivers and the like.
A plasma display device includes, as main components, a plasma display panel and a shield case that encloses the plasma display panel.
This plasma display panel is a display in which ultraviolet rays generated by gas discharge excite phosphors to emit visible light as display light. In the plasma display panel, a plurality of electrodes (display electrodes and address electrodes) are arranged in a grid pattern, and discharge cells formed at respective intersections of these electrodes are made to emit light selectively. Thereby, images are formed. Based on this principle, when a drive current flows through the electrodes, this drive current generates an electromagnetic field in the plasma display panel.
The shield case encloses the plasma display panel by connecting, with conductive glass pressing pieces, a front glass attached with a conductive filter and arranged in front of the plasma display panel and a conductive back cover arranged behind the plasma display panel. Thereby, the generated electromagnetic field is shielded electromagnetically.
A contact impedance exists at each contact portion between the respective components of the shield structure. When this contact impedance increases due to poor contact between them, the shielding performance of the shield case is degraded.
As a specific example of a conventional shield structure in such a plasma display device, JP 11(1999)-272183 A discloses a structure in which glass pressing pieces and another member are integrated into one unit so as to reduce the contact impedance.
However, the above-mentioned conventional structure, in which the glass pressing pieces press the four sides of the front glass from the back surface side thereof to hold it, as disclosed in JP 11(1999)-272183 A, has the following problems.
As shown in FIG. 8, a frame 9 is arranged in front of the front glass 5 along the four sides thereof. Specifically, the front glass 5 is sandwiched between the frame 9 and glass-pressing metal pieces (glass pressing pieces) 30 so as to be held between them. A resin molded component usually is used for this frame 9 in terms of design flexibility and cost reduction. This resin molded component is, however, lower in strength than a metal. Therefore, when the front glass 5 is pressed by the glass-pressing metal pieces 30 from the back surface side thereof, the frame 9 is deformed, which causes poor electrical contact between the front glass 5 and the glass-pressing metal pieces 30. As a result, the electromagnetic field shielding effect of the shield case is deteriorated.